WARNING: SHOCK HAZARD -
FIRST UNPLUG THE LATHE MOTOR FROM THE 110VAC OUTLET

EO Sensor
PlacementSpindle housing shown with the front cover removed. Cleaned the spindle
(sandpaper, steel wool, then alcohol) &
placed a piece of electrical tape, length-wise. Primed & then painted the
spindle flat black. Removed the
tape
leaving
a shinny area.
I used a
variable 4.7K ohm resistor &
two wire leads from the circuit to facilitate adjustment.
Before installing, I
reproduced the lathe install geometry by placing an aluminum cylinder
with a piece of black
electrical tape on it into a drill
press chuck. Then mounted, instrumented (voltmeter) & pre-tweaked the circuit
to get
it working reliably.
Mounted the reflective tachometer pick-up off one
of the bolts.
The cable loops over the spindle. The IR sensor
is the Fairchild QRB1114.

For the DPU-550, a 74LS14 Schmitt Trigger was needed
to make this particular tachometer
setup work
reliably.
The IC (unused pins removed) was spliced into the AUX IN of the header wires,
then shrink-wrapped. Diagram.
Pin 7 is ground, pin 14 is +5VDC, pin 1 is the signal IN from the sensor &
pin 2 is the signal
OUT to the DRO.
This circuit converts the sensor's somewhat noisy waveform to a clean,
well-defined, square-wave output.
The unused inputs do not have to be tied to ground because the purported power
loss is insignificant.

Objects that appear light or dark to the eye can exhibit either high or low
NIR reflectivity. This characteristic must be taken into account when selecting materials for use in NIR reflective
tachometer pick-up assemblies.For example, if the axle's black paint had high NIR reflectivity
(like the metal), it
would not have activated the sensor properly. This principle applies to all materials including: plastic,
metal, paint, tape, etc.Selecting a material based solely on its visual appearance can
lead to a sensing
failure.

CablePower switch housing cover was then removed. Routed the tachometer cable
through a pre-existing hole. Used
spiral
cable wrap, a cable tie-down & a grommet
to assure long-term vibration does not abrade the
shielded/grounded cable.

Surface Feet per MinuteSFM is only a starting point. When cutting metal,
one attends to (among other things):speed, feed, chip size,
chip length, chip coloration,coolant, rigidity, surface finish, sound,
smell, &
vibration.There are numerous, interacting variables that are unique to
any given machine & setup that simply
can not be accounted for by SFM tables.
The rigidity, coolant, & feed in a vertical machining center
is a bit better than a hand drill. So to say that one SFM value should be the
same for both is a stretch.

The DPU-550 DRO also calculates SFM. Now I can set
different speeds to
obtain a specific SFM
(e.g., 200) that varies as diameter changes.
Use Function 7 to toggle & assign which line Tach or SFM are to be displayed
on.